Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Therefore, the secondary battery is being applied to an increasing number of applications owing to advantages thereof, and, in the future, the secondary battery is expected to be applied to even more applications and products.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery module having a plurality of battery cells electrically connected to each other because high power and capacity are necessary for the middle or large-sized devices.
The size and weight of the battery module is directly related to the receiving space and power of the corresponding middle- or large-sized device. For this reason, manufacturers are trying to manufacture small-sized, light-weight battery modules. Furthermore, devices, such as electric bicycles and electric vehicles, which are subject to a large number of external impacts and vibrations, require stable electrical connection and physical coupling between components constituting the battery module. In addition, a plurality of battery cells are used to accomplish high power and capacity, and therefore, the safety of the battery module is regarded as important.
Preferably, the middle or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic lithium polymer battery or a pouch-shaped lithium polymer battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle or large-sized battery module.
However, the lithium polymer battery is relatively expensive due to a complicated manufacturing process thereof and exhibits relatively low use properties at a low temperature. Also, application of the lithium polymer battery to products having various sizes is limited. For this reason, the use of a cylindrical lithium ion battery has been attempted in recent years.
The cylindrical battery has great difficulty in maintaining arrangement as a stacked structure due to the appearance characteristics thereof although the cylindrical battery has a higher electric capacity than the prismatic battery or the pouch-shaped battery. For this reason, the use of additional fixing members is necessary for the cylindrical battery. For example, there has been normally used a method of arranging cylindrical batteries and fixing the cylindrical batteries with a fixing tape or coating cylindrical batteries with plastic so as to maintain the arrangement structure of the cylindrical batteries. According to circumstances, a double-sided adhesive tape may be attached between the cylindrical batteries so as to further increase coupling force between the cylindrical batteries.
However, the strength of the fixing tape and the plastic coating is small, and therefore, the fixing tape and the plastic coating may be easily damaged or broken. Consequently, the fixing tape and the plastic coating are not suitable for stably maintaining the arrangement structure of the batteries.
Furthermore, it is required for a battery module to have various outputs and capacities by adjusting the number batteries connected with each other depending upon the specification of a device in which the battery module is used. In the cylindrical batteries, however, a fixing member for maintaining the arrangement structure of the cylindrical batteries is requisite. Consequently, there is a problem that various kinds of fixing members must be manufactured depending upon the number of cylindrical batteries to be assembled when a battery module is constituted by the cylindrical batteries. In order to solve this problem, a unit fixing member may be manufactured such that one or two batteries can mounted to the unit fixing member, and a plurality of unit fixing members may be connected with each other to constitute a battery pack. In this case, however, it is necessary that the unit fixing members be coupled with each other depending upon desired output and capacity of the battery pack.
Consequently, the necessity of a technology for fundamentally solving the above-mentioned problem is very high.